Satellite communication systems are widely used to support video, voice and data communication services all over the world. In recent years such services are being delivered to the individual end-user directly via small fixed or mobile terminals on a point-to-point basis.
Handheld mobile terminals, and other ultra-small aperture personal terminals are expected to be widely used with all types of satellite systems for mobile and fixed telephony, data/fax, interactive bandwidth-on-demand, and multimedia applications.
All such satellite systems rely on the use of any one or a combination of single channel per carrier (SCPC), time-division multiple-access (TDMA) or code-division multiple-access (CDMA) transmission technologies. Such systems result in transmission of a large number of signal carriers in a frequency-division multiple-access (FDMA) arrangement, and on a demand-assigned multiple-access (DAMA) basis. In these systems each user is allowed to access and use the system only when the user has a need, and even then the system resources are assigned to the user based on demand. From the perspective of a satellite communication system, users do not have a dedicated full-time transmission channel but rather share such channels with other users. Moreover, signal transmissions from end-user terminals to the satellite do not need to occur unless there is information to be transmitted.
Examples of such satellite communication systems include geosynchronous (GSO) and non-geosynchronous (NGSO) earth orbit systems which are being deployed for mobile and fixed telephony applications, in addition to the new wide-band systems for bandwidth-on-demand and point-to-point multimedia services. To meet the business requirements for high-capacity and wide-area coverage capabilities, most such systems employ a large number of very high-gain spot beams.
In general, communications satellites can cover a large geographical area via a single or several communications beams (reaching even a few hundred beams in some cases). The total available radio frequency spectrum for each satellite beam is generally broken up into a number of smaller channels. Each radio frequency channel can be used, based on many system design objectives, to carry signals using any of the three transmission technologies (SCPC, TDMA, or CDMA) noted above. In demand-assigned systems, transmission of the signal carrier by each user terminal in any channel is managed by a central system controller. The power level of each carrier, and how much of the satellite downlink power is used by that carrier, is determined by many system parameters but is generally fixed once it is determined. However, such systems typically employ uplink power control to compensate for propagation anomalies so that the signal level received at the satellite is relatively constant.
On board the satellite, each downlink beam carries signals from one or more payload repeaters. Repeaters may be of the bent-pipe (transponder) or regenerative types, using analog or digital signal processing technologies. Each repeater may have a dedicated high-power amplifier (HPA) or share a hybrid-matrix amplifier assembly with other repeaters. Each repeater may also be assigned to a single signal carrier or be used to support several carriers. All such high-power amplifier assemblies supporting multiple carriers are operated in a linear mode.
The total downlink power of each satellite is divided among its repeaters based on the projected traffic capacity of each repeater. With bent-pipe designs, the repeater power is also pre-allocated to each carrier based on a maximum number of such carriers the repeater must support. In other words, a predetermined portion of the repeater power is always reserved for each signal carrier whether or not that carrier is actually present. With regenerative designs, where user traffic through each repeater is generally multiplexed into a single downlink time-division multiplexed (TDM) carrier, the repeater power is fully utilized at all times regardless of traffic volume. This guarantees the availability of power to each carrier (or user data burst) during heavy traffic periods when each repeater is expected to be loaded at its maximum capacity. However, as with all demand-assigned multiple-access transmission techniques, the peak system loading occurs only during a small fraction of the daily or periodic operations. Moreover, the peak traffic loading for each repeater usually occurs a few years after the system start when the full population of user terminals are deployed and operational.
As such, satellite based communication systems are deployed with a capacity to support a system which generally reaches its maximum traffic loading several years later. Even then, the full payload power of each repeater is utilized only for a small fraction of the time during the peak daily traffic hours. For all other times, the power of each repeater is reserved for many channels or carriers which are not active. Recognition of this gross under-utilization of the expensive satellite payload power provides significant opportunity for improvement as accomplished by the present invention.